The proposed system (a hardware-software assembly and the recognition methods) may be used on a large scale in the signature authentication procedure, with a minimum discomfort regarding the usage procedure and comparatively low costs. Therefore, the present invention creates the premises for the applications development in the information technology field in multiple social and individual interest areas.
The applicability domains of the system cover the following fields of interest:                Patrimonial, Financial transactions, etc. Function: link in checking systems;        Security in the field of virtual or physical access control systems. Function: link in security systems;        Companies and institutions management. Function: authenticating the signature in software applications of Document Management/Workflow Management type, for companies with a large number of employees or distributed staff. Protection of electronic documents.        
Applying the invention herein presented in these activity domains has the following results: it increases the user's level of trust in the above-mentioned fields, minimizing the losses due to the identity frauds, reducing the signature checking time in the domains where the classic procedures require this action, discouraging the frauds committed by forged identity.
In the invention's description, we shall use the following notions:
Subject: Person that uses the system for registering the sample signatures in the database, in order to authenticate an original signature or attempt to authenticate a forged one.
Signature: Represents the subject's action, consciously started, by free will but with a reflexive inherited motion character, by manually using a writing instrument and having a plane graphic result in a predetermined space. The subject commits to be able to reproduce this action proportionally from the spatial-temporal point of view. The signature's purpose is the subject's recognition based on the comparison between the sample signature and the original signature and admitting to a third party the action of deciding whether the signature is or not authentic.
The (signature's) (bio) kinetic pattern: The way the movements of the biomechanical assembly handwriting tools take place, in order to perform the signature. These movements are partially transposed under the form of the graphical signature, by the practical extremity of the writing instrument on normal writing paper, in usual document format of the public or private life. The (bio) kinetic pattern may be electronically acquired and memorized. The (bio) kinetic signature pattern notion assimilates with the signature notion.
Sample signature (herein shortly referred to as sample): Signature stored in a signatures database and used in order to subsequently certify (authenticate) a person that performs in this purpose a new signature (original signature).
Original signature (herein shortly referred to as original): Signature given by a person in order to be certified (authenticated) by the system, when compared with other signatures (sample signatures) formerly given by the same person—subject—and stored in a signatures database.
Forged signature (herein shortly referred to as forgery): Signature given by an X person that claims to be the Y person and signs in the name of Y or signature given by the X person who signs in the name of X but under constraint.
Authentication: Set of methods applied to the bio-kinetic patterns from the current base, by which it is determined whether the X person that signs in original is indeed the X person that signed the samples set (from the signatures database) that were registered as belonging to the X subject.
Current database: Initial database plus the bio-kinetic patterns of the subjects' samples and authenticated originals.
Current comparison database: Set of signatures formed of the samples of a number of subjects representing a specimen (randomly extracted) from the current database plus the signatures of the subject targeted by the entrance signature.
Initial database: The minimum database required for the system to function at the established parameters, containing the bio-kinetic patterns of the sample signatures belonging to the targeted orthographical culture (alphabet) (for example: Latin, Cyrillic, Hebrew, Chinese, etc.). The initial database may also contain the bio-kinetic patterns of the signature samples belonging to mixed orthographical cultures.
Level: Physical and functional hierarchy within the authentication system, containing specific functional subsystems and the method structures housed by said systems.
Pen: Ensemble composing the level 1 subsystem, composed by the writing device and the sensitive-kinetic-computer based elements required for capturing the bio-kinetic pattern.
MEMS (micro-electro-mechanical-systems): micro-sensitive-electro-mechanical-system realized by nanotechnology.
Contact Information: Biometrical information incorporated in the signature, required to delimitate the signature. It manifests because of the synaptic neuromotor reflex mechanism, representing the modulation of the micro-vibrations generated by the interaction of the subject with the paper, by means of the pen. The MEMS sensors capture it, on the manifestation directions. The biometrical information is intrinsically mixed with the other bio-kinetic information specific to voluntary or semi-reflex writing.
Context information: Information regarding the manner the pen is positioned near the writing paper. It is expressed by the detection of a threshold distance to the paper, being one of the keys required to delimit the signature from other kinetic actions of the subject.
When it is required to authenticate a signature, specialized people perform the classic procedure. The analysis and decision action regarding a handwritten signature's authenticity represents one of the objects of the graphology technical expertise science. In order to establish a signature's authenticity, the person endowed with this function uses graphical and static projections of the signature performing complex action, in the paper plan. Following the analysis, there are deduced dynamic actions specific to the subject that performed the signature, materialized in the type of characteristic speed, acceleration, pressure, sequences and shapes.
Authenticating the handwritten signature in the classic manner has the following disadvantages, among others:                It contains a certain error quotient, statistically expressed and depending, among others, on the momentary analysis capacity of the person charged to check the signature;        It may be influenced by external factors, such as the expert interest or self-partiality;        It requires a rather long period of time of measurement, analysis, comparison and decision;        It arbitrarily presumes as true, the free-will expression;        The information is only extracted from the paper plan level and it unilaterally reflects only the graphical effects of the subject action;        The physic units speed, acceleration, pressure and the specific invariant graphic shapes, are indirectly deduced, by visual observation and deduction, procedures that imply a high level of approximation;        The spatial information, corresponding to the complex kinetic of the movements transmitted to the writing tool by acquired reflex gestures, by the specific hand geometry and synaptic type neuromotor interactions, is ignored;        The required experience and knowledge from the graphological expertise field is transmitted with considerable efforts and, is refined after a long period.        Regarding the classic graphological technical expertise for signature authentication, its price is several times superior to an automatic checking and practically it can take place only after the fraud's negative effects are produced and tracked down.        
The studies and investigations in the field of the automatic authentication based on the bio-kinetic pattern represent an alternative, recently approached domain of biometry. The efforts target the developing of authentication technologies, which are necessary to the informational society. The handwritten signature is used as a quasi-universal way to identify and authenticate alphabetized people. Therefore, the authentication methods based on the signature's bio-kinetic pattern are natural, normal, and non-intruding.
There are few studies in the specialty literature referring to the authentication procedures based on the bio-kinetic pattern. There are mainly some patents on this theme. Until now there is no information about any commercial applications based on acceleration sensors realized by MEMS nanotechnology and using the principles and methods of the present invention, implemented on the signature authentication purpose. The problem was approached only at a laboratory level and until now there has been performed little research upon this subject worldwide.
There are granted patents for authentication systems that analyze static and/or dynamic features of the handwritten signature. The ones that analyze the dynamic characteristics are more performant than the former ones, analyzing only the static characteristics.
Presently, there are commercial applications in the handwritten signature analysis authentication field, that use methods and technologies different from the one proposed by the invention herein presented: the graphics table, graphic scanning and certifying, dynamic capture of graphic images with CCD sensors, writing on “intelligent paper” based on standing markers. These solutions maintain some of the disadvantages mentioned in the case of human graphical expertise, namely:                The information subjected to analysis is extracted only from the paper plane level and it unilaterally reflects just the graphic effects of the subject's action;        The parameters: speed, acceleration, pressure, are indirectly deduced by procedures that imply a high level of approximation;        The spatial information is ignored corresponding to the complex kinetic of the movements transmitted to the writing tool by acquired reflex gestures, by the specific hand geometry and synaptic type neuromotor interactions.        
In addition to these disadvantages, the mentioned solutions introduce dedicated adjacent devices: the graphics table, intelligent paper, scanner, thus increasing the costs and the complexity of exploit.
There are few patents in the field of biometrical authentication based on bio-kinetic pattern of handwritten signature describing systems and methods which, by the nature of the analyzed parameters or the way of acquisition and processing, are tangent to the present invention. As reference for comparison and for defining the claims in the present invention, we quote two of these patents considered as relevant: U.S. Pat. No. 4,128,829—(Herbst et al) and U.S. Pat. No. 6,236,740—(Lee et al.).
In the U.S. Pat. No. 4,128,829—(Herbst et al) the information is generated by two acceleration sensors orthogonally positioned in the pen and an axial pressure sensor. The information is digitized at an 8-bit resolution in an exterior module of the pen. The comparisons between the signatures are realized by information segmentation and seeking the maximum crossed correlation. The final decision is of the threshold type, the acceptance or the rejection depending on the position of the correlation answer's value against an arbitrarily chosen threshold (0.8). The decision is taken after the comparison between the entrance signature and the targeted subject's sample signature.
The following disadvantages remain in this patent:                The information corresponding to the complex spatial kinetic of the movements transmitted to the writing tool is ignored, as the acceleration sensors are at a single plane level;        The information corresponding to the synaptic type neuromotor interaction is lost, on one hand because Herbst pleads that the neuromuscular feedback is exclusively performed by the slow “muscle-brain-muscle” cycle, ignoring thus the effects of the local synaptic reflex, at the hand bio-functional level; on the other hand, its system acquisition and post-processing parameters don't allow the acquisition of the synaptic reflex specific information;        Using an axial pressure sensor partially and indirectly regains the information corresponding to the lost synaptic type neuromotor interaction, but in the same time it introduces specific disadvantages such as inconsistent detection of the moments in which the subject establishes contact with the writing paper, the pressure's variability depending on: the way the subject is positioning when writing, paper type, etc.;        The threshold decision method is inflexible to the signature natural variability and even more, it is impossible to calculate a generally valuable threshold as it varies from one subject to another.        
In the U.S. Pat. No. 6,236,740—(Lee et al.) the analyzed entrance information is generated while performing two actions: the signature and the subject's performing an imposed set of digits: from 0 to 9 in case of samples and, of digits expressing the current date, in case of the signatures that are about to be authenticated. Two pressure sensors located in the pen capture the information to be analyzed, such that electrical signals, proportional to the pressure exerted in the writing peak, are acquired by mechanical elements. The two signals produced by the sensors represent the pressure discomposure on two pen directions: axially and laterally. The information's digitization takes place in an exterior module of the pen. The information analysis is processed upon a parameter defined by momentary ratio of the two pressures, named relative gradient angle and considered relevant in order to differentiate the signatures. The decision and analysis methods are performed by the threshold adaptable type of evaluation of the result of the comparison between the entrance signatures and several specimens of the targeted subject, including the imposed digits. The analysis methods combine the information segmentation and its global evaluation.
The following disadvantages remain in this patent:                The information corresponding to the plane and spatial kinetics of the movements transmitted to the writing tool is ignored, as there are no sensors to notice the pen movements. The information corresponding to the pen movement on the paper is indirectly and appreciatively transposed in the pressure information, which explains the maintenance of a certain functionality;        The constructive mechanical elements having direct functions on the sensors virtually diminish the reliability of the solution;        The digitization of the electrical signals containing the analyzed information outside the pen implies the possibility to affect them by external perturbations;        Using the pressure sensors approximately, partially and indirectly distinguishes the information corresponding to the synaptic type neuromotor local interaction and it also introduces specific disadvantages such as an inconsistent detection of the paper contact moments, pressure variability depending on the writing position, paper type etc.        The analysis and decision method is applied by evaluating the result of the comparison only between the entrance signature and the sample signatures of the targeted subject.        
The analysis, comparison and evaluation methods from the above presented inventions, apply only between the entrance signature and the specimen signature of the targeted subject. Therefore, the principle of category affiliation by the differentiation and manner to relate regarding the other categories, respectively comparing to other subject's samples as well, is ignored.
The herein presented invention removes the mentioned disadvantages by the new concept of realizing the acquisition device regarding the nature, signification and detection of the complex information generated during the signature process, by functionally integrating the subsystem that forms the acquisition device in a computer based authentication device.
The algorithmic methods and the procedures implemented in the computer based authentication system by specific programs, indissolubly related with the processed entrance information, apply not yet exploited principles from this science field and considerably improve the methods of the already applied principles.
The main impediment that maintained the lack of commercial potential applications, based on the spatial bio-kinetic analysis, has been until recently the lack of necessary technologies, namely the absence of MEMS acceleration sensors (http://www.memsnet.org), sufficiently miniaturized and performant, for a satisfactory capture of the complex accelerations produced to the writing instrument, by the hand, during usage. From the cost point of view regarding the information acquisition by accelerometer type sensors, until 2002, the costs were well beyond the limits of the commercial efficiency for a single acquisition channel as, in order to obtain quality information, there are necessary multiple acquisition channels. From the commercial efficiency point of view, the MEMS acceleration sensors allow conceiving acquisition devices/systems at competitive prices. At the end of 2001. The Nanotechnology Research Centers MIT and Analog Devices realized and launched in production a MEMS acceleration sensor with superior quality-price performances; therefore this research action was started off and the result is the object of the herein presented invention, targeting usage of this new type of sensor. Another research project XWPEN, based on the same technology (from the point of view of the sensors that were used), carried out in the Microsoft Hardware Research laboratories, studied another application (a terminal for handwritten input and recognition), did not reveal to the public the specific technical elements and it aimed at obtaining applicable results by the end of the year 2004.
The sensitivity of the MEMS nanotechnology sensors is of mg class, with a μg/√Hz (g=gravitational acceleration) noise factor class. Grace to the sharp sensibility and the frequency characteristics, these sensors fulfill the conditions required to be included in the construction of the new capture devices/systems for the slightest informational components of the handwritten signature bio-kinetic pattern. It is also to be mentioned that in the herein invention there are used MEMS sensorial modules; each of them integrating, by construction, two acceleration sensors, orthogonally located with respect to one another.
In the herein presented system, the assembly of movements required to realize the handwritten signature transmitted to the writing device define the kinetic pattern of said signature and, implicitly, the person's. The kinetic pattern contains informational structures specific to the person that performs them. The high complexity of these informational structures, because of the physical parameters that might shape them, their dynamics and context variability, practically excludes the possibility to determine a metric defining pattern. The graphic shapes and tracks impressed on the paper may be considered an incomplete and conjectural projection, in the paper plane, of the assembly of these movements, acting like a reflex visual feedback, necessary to perform the mentally intended action—the signature.
The writing paper is made up, among others, of cellulose micro fibers. Their randomly disposal creates asperities at a microscopic level. At macroscopic level, the disposal of asperities in the paper plane is constant, this property being imposed by the technologic process for making the paper, according to the standards in the field. During the writing action, due to the interaction between the paper and the usable extremity of the writing tool, it appears a mechanical quasi-resonance phenomenon with frequencies that depend on the writing speed, manifested by mechanical micro vibrations. These micro vibrations also propagate in the writing tool body. The more the phenomenon tends to harmonic resonance, the easier the writing process becomes. For example, this phenomenon may be noticed by the specific acoustic sound emitted during the writing process; we can write between “soft” and “scratch” extremes, fact that emphasizes the presence or absence of the mechanical quasi-resonance.
During writing, the mental model of the specific graphic symbols, combined with the hand biomechanical geometry, imposes a momentary variable speed. The effect of this speed variation tends to damp the previously reached quasi-resonance. In this context the action of the synaptic neuromuscular reflex (“Basal Ganglia & Motor Control for JA2084”, Malcom Lidierth, November 2004, University of London—Academic Department of Anatomy and Human Sciences JA 2084 Fundamentals of Neuroscience) becomes effective by producing biomechanical micro-actions in the sense of re-entering the quasi-resonance state. This accommodation mechanism unconsciously takes place at any momentary speed variation. The synaptic neuromotor cycle generates the accommodation micro-actions, lasting only few milliseconds. The adjustment loop requires few cycles in order to obtain a momentary quasi-stability; respectively, 20-60 ms. The biomechanics correspondent phenomenon is named force-feedback.
The biomechanical micro actions generated by the synaptic reflex are transmitted to the writing extremity by the pen body, regaining the quasi-resonant micro vibrations necessary for an easy writing. The micro vibrations are transmitted by the constructive pen elements, especially created and positioned for this action and orientedly captured by the two acceleration sensors orthogonally placed in each MEMS module. The biomechanical micro actions are revealed by the other kinetic specific to writing by the micro vibration filtering methods. The valuation of the variability of the micro actions, by algorithmical methods that we shall further on describe, revealed an essential invariants category which generates specific “patterns” for every subject's signature. The invariants are the “pattern” expression for the neuromotor bioelectrical signals of the synaptic reflexes. The pressure is appreciatively derived for the described phenomenon and, therewith, appreciatively integrated through the hysteretic specific to the pressure sensors; therefore, it is not used as principle for this invention.
Along with the described role, the micro vibration's detection is also necessary, as it will be further described in the algorithmic method, to establish the signature's start and finish moments, as well as the pause moments during the signing process. The procedure and the mechanism required for context information analysis are introduced in order to avoid the false start detections. Based on optical type information, it can be detected whether the pen is or not in writing position, thus avoiding the false rendering of accidental vibrations generated by handling the pen foregoing to the signature.
The spatial bio-kinetic pattern is physically sampled by acquiring the accelerations amplitudes which are simultaneously sampled in several points of the writing device main axis, thus facilitating the capture of the balance spatial centripetal components, comparing to the virtual and dynamic center of the balance movements necessary for the writing action. The information digitization is possible with a sample rate high enough to capture the frequencies corresponding to the “acquired reflex” character movements required for the writing activity (2-10 Hz) and therewith to capture the frequencies specific to the local neuropsychomotor cycles —the synaptic reflex (10-50 Hz). Due to the filtering methods of the components corresponding to the vibrations, specific shapes to the synaptic cycles are retained in the digitized signals. The digitized biokinetic pattern will contain composed combinations of invariants specific to the acquired calligraphic gestures and reflexes, invariants specific to the hand's physiology, synaptic reflexes and last, but not least, invariants specific to the personality of the person that performs the signature.
The biometric character of these invariants is a proven fact, as their projection at the paper level represents the entrance information for the graphological expertise. The spatial biokinetic patterns acquisition and analysis and the invariants determined by the biokinetic information combination, generate information sets that allow a much more far-reaching analysis of the signature authenticity, comparing to the classic situation when only a single informational category—classically, the imprints from the paper level—is subjected to analysis. The implicit or refined set of invariants series and the primary or derived set of signals, obtained by methods that will be further described, represent a synthetic decryption of the initial signature informational structure. The accuracy level of the decryption depends on the acquisition subsystem sensitivity and the profoundness of the signals analysis that compose the signature kinetic pattern refining process. The system final answer reflects in the comparison methods accuracy and depends on the signatures stability.
This system's advantages, compared with other authentication methods and systems are:                A close correlation between the person and the analyzed information (the dynamic signature features are characteristic to a certain person and they cannot be easily forged). These features correlate with the free will expression of the person that agrees on something by signature. The fact that the human being does not naturally possess specialized sense organs for the fast dynamic acceleration perception makes difficult any conscious analysis and reproduction in forging purposes, as it is correlated only with the graphical aspect;        The psychological studies show that performing actions immediately perceptible by the subject, among which the signature, represents a natural auto projection mechanism of the individuality regarding the third parties. Therefore, the subject having a correct identity and a real authentication interest, will not consider the system as intrusive;        
The handwritten signature authentication method (based on graphic aspect, deducing the writing pressure profile, or the acceleration from the graphic symbols thickness variability) is already used and it is considered less intrusive than other authentication methods (iris scanning, finger prints, DNA test);                The biokinetic information is acquired with a device conceived similarly to an usual pen as shape and size, which includes, along with the kinematic sensorial structures, a microcontroller block for data digitization and transmission to the physic levels that host to the algorithmic processing methods;        The system does not require signing on especially conceived support-devices (the graphic tablet) or intelligent paper with included navigator markers (for example the Anoto Pen). The signature may be performed naturally, on any usual writing document type;        The information input into the system is devised and based on nanotechnology area sensorial systems—MEMS accelerometers—emphasizing their benefits: reliability and sharp accuracy, minimum price and dimensions;        The starting and finishing signature detection method is based on the information corresponding to the contact micro vibrations, analyzed in parallel with the context information;        The system functioning in authentication regime implies activating the initial database required to apply the implementing method and the principle of establishing the category affiliation by the way of differentiation and relating to all the other categories. In this method context, a category is constituted by the specimens of virtual subjects, representative for the targeted orthographical culture;        There are two methods (algorithms) for processing, analyzing and comparing the information: SRA1 and SRA2, independent with respect to one another, by the algorithmic and data pre-processing principles. The results of the two independent methods represent entrances for the final decision method and a feedback for eventual current signature database enrichment and updating. The information represents data structures resulted from composing and pre-processing the spatial kinetic information, the contact information that describes the biomechanical micro-actions generated by the synaptic reflex, and the information that delimits the signature;        The method for adjusting the system confidence level and for diminishing the system answering time which is realized by shifting and implementing the mathematical principles for statistical error control of the quality control area.        
The system's answer intrinsically relates to all the signature specimens existing in the current comparison database, by the used analysis and comparison methods. Thus, the principle of establishing a category affiliation by way of differentiation and relation to all other categories, is observed, by comparing the entrance signature with the samples of all the other subjects from the current database, minimizing the system's dependence on the cultural-orthographical specificities of the population for which it is used, respectively. Also, by this method, the disadvantages of the decision based on global or adaptable threshold authenticity evaluation, specific to other domain related inventions, are removed.